I have some stuff on real splines (their similarity and difference from the mathematical idealization) in section 3.12 of my thesis (page 39 of https://www.levien.com/phd/thesis.pdf).

There's also a bunch of stuff in there about Euler spirals (aka clothoids), including application to railways - see section 6.6, page 106. Fun fact, I'm going to get my first tattoo soon, and it will be an Euler spiral.